Sporadic E

50 and 144 MHz signals are often propagated over distances up to 1400 miles, sometimes with exteremely strong
signals by Sporadic E (or Es). When conditions are good even very small stations can make contacts (Editor's note:
I remember during one opening on 144 MHz in 1989, working a station in W4 land who was running 2 watts with a portable
transceiver, using just the whip antenna built into the rig... his signal was well over S9 here in Maine). Multiple
hop Es does occur at times, and contacts out to 6000 miles have been made on 50 MHz, 1800 miles or more on 144
MHz. A very few contacts on 220 MHz have been reported, the first in 1987.

At mid-latitudes, Sporadic E may occur at any time, but is most common in the northern hemisphere during May,
June, and July with a less intense season in late December/early January. Sporadic E is not directly linked to
the solar cycle. Peak times are 9 am to noon, and 5 to 8 pm. Openings may be very short, lasting only a few minutes,
or may persist for several hours. Interestingly, Sporadic E is an almost constant thing in the polar regions at
night, and in the equatorial region during the day. Sporadic E at VHF tends to be very selective geographically.
Often just 5 or 10 miles makes the difference between hearing a station very well and not hearing it at all.

The causes of Sporadic E are not well understood, and efforts to predict it have not met with much success.
Studies indicate that thin, dense patches of ionization in the E layer are responsible for the phenomenon. Sporadic
E clouds can form suddenly and sometimes move quickly before dissipating.

The Sporadic E MUF may start out in the upper HF region (21/28 MHz) and slowly or rapidly rise into the VHF
bands. Very short skip, on the order of 250 to 300 miles on 28 MHz may be a good indicator that the MUF has reached
50 MHz. Short skip of 400 to 500 miles on 50 MHz may indicate an MUF high enough to support 144 MHz contacts. Es
openings at 144 MHz are rare compared to 50 MHz, and usually do not last long. However, it is worth waiting for!

Editor's note:
Several good methods of spotting Sporadic E openings have been developed. At 50 MHz, the phenomenon is so common
a few missed openings may be no big deal, but at 144 MHz the next opening could be a long way off. My favorite
method is to monitor a locally clear channel at the low end of the FM broadcast band (say 88 to 95 MHz)... when
distant stations suddenly pop up there, I stick closer to the rig and begin monitoring a clear channel near the
top of the FM band, at 106 to 108 MHz. When the MUF reaches that high, it is time to start calling CQ on 144.200!

QRM on a 144 MHz Sporadic E Signal. This illustrates the selective nature of VHF Sporadic E.
The local GM6 station couldn't hear CN8ST, even though GM4JJJ was hearing him. Very typical.
Provided by GM4JJJ